On 17-01-19 15:14, Tom de Vries wrote:
> On 17-01-19 01:35, Ian Lance Taylor wrote:
>> On Wed, Jan 16, 2019 at 4:17 PM Tom de Vries <tdevr...@suse.de> wrote:
>>>
>>> this handles DW_FORM_GNU_ref_alt which references the .debug_info
>>> section in the .gnu_debugaltlink file.
>>>
>>> OK for trunk?
>>>
>>> Thanks,
>>> - Tom
>>>
>>> On 11-12-18 11:14, Tom de Vries wrote:
>>>> 2018-12-10 Tom de Vries <tdevr...@suse.de>
>>>>
>>>> * dwarf.c (enum attr_val_encoding): Add ATTR_VAL_REF_ALT_INFO.
>>>> (struct unit): Add low and high fields.
>>>> (struct unit_vector): New type.
>>>> (struct dwarf_data): Add units and units_counts fields.
>>>> (read_attribute): Handle DW_FORM_GNU_ref_alt using
>>>> ATTR_VAL_REF_ALT_INFO.
>>>> (find_unit): New function.
>>>> (find_address_ranges): Add and handle unit_tag parameter.
>>>> (build_address_map): Add and handle units_vec parameter.
>>>> (read_referenced_name_1): Handle DW_FORM_GNU_ref_alt.
>>>> (build_dwarf_data): Pass units_vec to build_address_map. Store
>>>> resulting
>>>> units vector.
>>
>>
>>>> @@ -281,6 +283,10 @@ struct unit
>>>> /* The offset of UNIT_DATA from the start of the information for
>>>> this compilation unit. */
>>>> size_t unit_data_offset;
>>>> + /* Start of the compilation unit. */
>>>> + size_t low;
>>>> + /* End of the compilation unit. */
>>>> + size_t high;
>>
>> The comments should say what low and high are measured in, which I
>> guess is file offset. Or is it offset from the start of UNIT_DATA?
>> Either way, If that is right, then the fields should be named
>> low_offset and high_offset. Otherwise it seems easy to confuse with
>> function_addrs, where low and high refer to PC values.
>>
>
> Done.
>
>> Also if they are offsets from UNIT_DATA then size_t is OK, but if the
>> are file offsets they should be off_t.
>>
>
> AFAIU, in the case where off_t vs size_t would make a difference, we're
> running into trouble much earlier. I've filed PR 88890 - "libbacktrace
> on 32-bit system with _FILE_OFFSET_BITS == 64" (
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88890 ) about this.
>
> Anyway, I've made the conservative choice of using off_t for now (but I
> could argue that it's a memory offset, given that the assumption is that
> the entire debug section is read into memory).
>
>>>> @@ -2144,6 +2198,22 @@ read_referenced_name_1 (struct dwarf_data *ddata,
>>>> struct unit *u,
>>>> || val->encoding == ATTR_VAL_REF_UNIT)
>>>> return read_referenced_name (ddata, u, val->u.uint, error_callback,
>>>> data);
>>>>
>>>> + if (val->encoding == ATTR_VAL_REF_ALT_INFO)
>>>> + {
>>>> + struct unit *alt_unit
>>>> + = find_unit (ddata->altlink->units, ddata->altlink->units_count,
>>>> + val->u.uint);
>>>> + if (alt_unit == NULL)
>>>> + {
>>>> + error_callback (data,
>>>> + "Could not find unit for DW_FORM_GNU_ref_alt", 0);
>>
>> s/Could/could/
>>
>> or maybe just skip this error_callback call as discussed earlier.
>>
>>
>
> Skipped.
>
>>>> + return NULL;
>>>> + }
>>>> + uint64_t unit_offset = val->u.uint - alt_unit->low;
>>
>> Earlier a unit_offset was the offset of the unit within unit_data, but
>> here this is an offset within a single unit. This should just be
>> called offset, which is the name used by read_referenced_name.
>>
>
> Done.
>
>> This is OK with those changes.
>
> Committed in two parts.
>
> First part ...
>
And second part.
Thanks,
- Tom
[libbacktrace] Handle DW_FORM_GNU_ref_alt
Handle DW_FORM_GNU_ref_alt which references the .debug_info section in the
.gnu_debugaltlink file.
2018-12-10 Tom de Vries <tdevr...@suse.de>
PR libbacktrace/82857
* dwarf.c (enum attr_val_encoding): Add ATTR_VAL_REF_ALT_INFO.
(read_attribute): Handle DW_FORM_GNU_ref_alt using
ATTR_VAL_REF_ALT_INFO.
(read_referenced_name_from_attr): Handle DW_FORM_GNU_ref_alt.
---
libbacktrace/dwarf.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/libbacktrace/dwarf.c b/libbacktrace/dwarf.c
index 6f56c46774b..aacbd3a453d 100644
--- a/libbacktrace/dwarf.c
+++ b/libbacktrace/dwarf.c
@@ -143,6 +143,8 @@ enum attr_val_encoding
ATTR_VAL_REF_UNIT,
/* An offset to other data within the .dwarf_info section. */
ATTR_VAL_REF_INFO,
+ /* An offset to other data within the alt .dwarf_info section. */
+ ATTR_VAL_REF_ALT_INFO,
/* An offset to data in some other section. */
ATTR_VAL_REF_SECTION,
/* A type signature. */
@@ -858,7 +860,7 @@ read_attribute (enum dwarf_form form, struct dwarf_buf *buf,
val->encoding = ATTR_VAL_NONE;
return 1;
}
- val->encoding = ATTR_VAL_REF_SECTION;
+ val->encoding = ATTR_VAL_REF_ALT_INFO;
return 1;
case DW_FORM_GNU_strp_alt:
{
@@ -2200,6 +2202,19 @@ read_referenced_name_from_attr (struct dwarf_data *ddata, struct unit *u,
|| val->encoding == ATTR_VAL_REF_UNIT)
return read_referenced_name (ddata, u, val->u.uint, error_callback, data);
+ if (val->encoding == ATTR_VAL_REF_ALT_INFO)
+ {
+ struct unit *alt_unit
+ = find_unit (ddata->altlink->units, ddata->altlink->units_count,
+ val->u.uint);
+ if (alt_unit == NULL)
+ return NULL;
+
+ uint64_t offset = val->u.uint - alt_unit->low_offset;
+ return read_referenced_name (ddata->altlink, alt_unit, offset,
+ error_callback, data);
+ }
+
return NULL;
}
